The present invention relates to a positive resist composition containing an alkali-soluble hydroxy-polyamide which functions as a precursor for heat-resistant resin material; to a hydroxypolyamide suitable for use in the composition; and to a method for formation of a heat-resistant pattern using the positive resist composition.
Polyimide resins superior in heat resistance, electrical properties, mechanical properties, etc. have heretofore been used in the surface protective film and interlayer dielectric of semiconductor device. These polyimide resins are generally provided in the form of a photosensitive polyimide precursor composition, can easily form a pattern by subjecting the composition to treatments such as coating, patterning by actinic ray, development, thermal imidization and the like, and have the feature that they allow for significantly fewer operational steps as compared to conventional light-insensitive polyimides.
In the development step of the photosensitive polyimide precursor composition, it is necessary to use a large amount of an organic solvent (e.g. N-methyl-2-pyrrolidone) as a developing solution. Due to the increased concern in recent years for environmental problems, a measure for developing without the use of the organic solvent is being sought. In this connection, various proposals have recently been made for a heat-resistant photosensitive resin material which is developable with a dilute aqueous alkali solution similarly to photoresists.
Of these proposals, a method using an aqueous alkali-soluble hydroxypolyamide (e.g. polybenzoxazole (PBO) precursor) in combination with a photoactive component (e.g. quinone diazide) has drawn attention in recent years (JP-A-63-96162, etc.).
These resins can easily form a positive pattern when subjected to light exposure and development with an aqueous alkali solution, have good developability and storage stability, and exhibit heat-cured film properties equal to those of polyimides; therefore, they are drawing attention as a promising substitute material for organic solvent-developable polyimide precursor. However, the PBO precursors developed by the methods disclosed heretofore have a number of problems.
In general, the PBO precursor is obtained by polycondensation between a hydroxydiamine and a dicarboxylic acid or a derivative thereof, but ordinarily has an amino group at the polymer terminals for the polymer stability and handling. A PBO precursor having amino groups at the terminals, however, has a problem in that it deteriorates the diazoquinone compound used together as a photosensitive material in a positive resist composition and greatly reduces the stability of the composition. In order to alleviate this problem, it was proposed to modify the terminal amino groups. For example, it was proposed to block the terminal amino groups in the form of an aromatic amide by using benzoyl chloride or the like, though this proposal was made for a negative composition (see JP-A-7-128846). When such a polymer whose terminals are simply blocked in the form of an aromatic amide, is used in a positive composition, the positive composition has improved stability; however, the cured film obtained from the composition is very weak and has problematic mechanical properties. In order to alleviate the problem, there was proposed a method of modifying the polymer terminal groups with a unsaturated bond-containing group such as alkenyl (e.g. norbornene), alkynyl or the like (see JP-A-5-197153). Certainly, with this method, the resulting composition has improved stability and, after the heat-curing of the composition, the unsaturated bond-containing group gives rise to formation of a network structure and consequent formation of a film superior in mechanical properties and adhesivity. Such a method of introducing an unsaturated group into polymer terminals has been widely used in thermosetting polyimides, etc.; however, the linkage formed thereby takes a form in which aliphatic chains are connected and, therefore, is generally insufficient in heat resistance. For example, when subjected to a heat treatment at a high temperature of 350xc2x0 C. or higher, the linkage is cleaved, thereby resulting in a significant reduction in film properties and adhesivity to the base material. The lack of reliability is a big problem when the polymer is used as a protective film for a semiconductor device.
The increased integration of electronic parts such as semiconductor integrated circuits and the like is striking, and the wiring structure employed in such parts has become more multilayered. In that connection, the reproducibility of the pattern in heat-curing of the interlayer dielectric and/or surface protective film has become more important. In using a PBO precursor-containing positive resist, however, no film fully satisfactory in pattern reproducibility is obtained during the thermal treatment.
As in conventional cases, polymer flow takes place during curing and there appears a problem of pattern deformation, for example, covering of the pattern bottom or decrease in opening area of the pattern bottom.
(1) The present invention aims at providing a heat-resistant positive resist composition which can form a positive pattern by light exposure and development with an aqueous alkali solution, which is highly stable even when combined with a diazoquinone compound, and which satisfies at a high level the heat resistance and dynamic properties required for use in the surface protective film and interlayer dielectric of semiconductor device; and a hydroxypolyamide suitably used in such a composition.
(2) The present invention also aims at providing a positive resist composition capable of giving a pattern significantly improved in shape deformation when heat-cured.
(3) The present invention further aims at providing a method for forming a heat-resistant pattern by using the above positive resist composition.
The present inventors made an intensive study in order to achieve, by paying attention to the terminal groups of a hydroxypolyamide used as an alkali-soluble PBO precursor in a positive resist composition, the prevention of deterioration of a diazoquinone compound used in the positive resist composition together with the hydroxy-polyamide and further the formation of a film superior in heat resistance and other properties. As a result, the present inventors found out that the above task (1) could be achieved by converting the terminal amino groups of the hydroxypolyamide into terminal groups of a particular structure.
The present inventors also found out that the above task (2) could be achieved by allowing the hydroxypolyamide having particular terminal structures, to have a particular polymer structure which shows no glass transition temperature (Tg) at least at 400xc2x0 C. or below, that is, has a Tg higher than the curing temperature.
The first aspect of the present invention is a positive resist composition comprising a hydroxypolyamide represented by the following general formula (I) and a photoactive component: 
(wherein R1 and R3 may be the same or different and are each a tetravalent aromatic group; R2 is a bivalent aromatic group; n is an integer of 2 to 150; and Z is a monovalent organic group and at least 40% of Z is a group represented by the following structural formula (II):
xe2x80x94Xxe2x80x94R4xe2x80x94(COOH)mxe2x80x83xe2x80x83(II)
wherein X is a carbonyl group or a sulfonyl group; m is an integer of 0 to 3 with a proviso that m is not 0 when X is a carbonyl group; R4 is an aliphatic group not including alkenyl group or alkynyl group, an alicyclic group or an aromatic group; and, when X is a carbonyl group and R4 is an alicyclic group or an aromatic group, at least one of the carboxylic groups is at the ortho position).
As the photoactive component used herein, a photosensitive diazoquinone compound is preferred.
In the first aspect of the present invention, the X in the structural formula of the Z of the general formula (I) is particularly preferably a sulfonyl group because excellent mechanical properties are exhibited at temperatures lower than 350xc2x0 C., for example, even at 320xc2x0 C.
In the general formula (I) of hydroxypolyamide, R1 and R3 are each preferably the following group because there can be obtained a positive resist composition capable of forming a pattern significantly improved in shape deformation during heat curing: 
The second aspect of the present invention is a hydroxypolyamide suitably used in the positive resist composition of the above first invention and is a hydroxypolyamide represented by the following general formula (III) (the second invention): 
(wherein R1 and R3 may be the same or different and are each a tetravalent aromatic group; R2 is a bivalent aromatic group; n is an integer of 2 to 150; and Z is a monovalent organic group and at least 40% of Z is a group represented by the following structural formula (IV):
xe2x80x94Xxe2x80x94R4xe2x80x94(COOH)mxe2x80x83xe2x80x83(IV)
wherein X is a sulfonyl group; m is an integer of 0 to 3; and R4 is an aliphatic group not including alkenyl group or alkynyl group, an alicyclic group or an aromatic group)].
The third aspect of the present invention is a method for forming a heat-resistant pattern (the third invention), which comprises coating, on a semiconductor device, the positive resist composition of the first invention, then subjecting the coated material to prebaking, light exposure and development for patterning, and heat-curing the resulting coating film pattern.